1. Field of the Invention
The present invention relates to a data transfer control device, an information storage medium, and electronic equipment, and, in particular, to a data transfer control device, an information storage medium, and electronic equipment for performing data transfer that is based on a standard such as IEEE 1394 between a plurality of nodes that are connected by a bus.
2. Description of the Related Art
An interface standard called IEEE 1394 has recently been attracting much attention. This IEEE 1394 lays down standards for high-speed serial bus interfaces that can handle the next generation of multimedia devices. IEEE 1394 makes it possible to handle data that is required to have real-time capabilities, such as moving images. A bus in accordance with IEEE 1394 can be connected not only to peripheral equipment for computers, such as printers, scanners, CD-RW drives, and hard disk drives, but also to domestic appliances such as video cameras, VCRs, and TVs. This standard is therefore expected to enable a dramatic acceleration of the digitalization of electronic equipment.
Under this IEEE 1394, an event called a bus reset occurs when new electronic equipment is connected to the bus, electronic equipment is removed from the bus, or the number of nodes connected to the bus increases. When a bus reset occurs, the topology information relating to the nodes is cleared then this topology information is automatically reset. In other words, after a bus reset, tree identification (determination of the root node) and self identification are performed, then the nodes that are to act as management nodes, such as the isochronous resource manager, are determined. Ordinary packet transfer then restarts.
Since the topology information is automatically reset after a bus reset under this IEEE 1394, it is possible to plug in cables in a state called a hot state (hot-plugging). For that reason, it makes it possible for a user to freely plug in cables in the same manner as with ordinary domestic electrical appliances such as VCRs, which could be a useful factor in popularizing home network systems.
However, it has become clear that there are some technical problems caused by the occurrence of such a bus reset with devices such as printers or scanners that are connected to an IEEE 1394 bus, as described below.
If a bus reset occurs during the transfer of print data on an IEEE 1394 bus, the initiator, such as a personal computer, restarts the transfer of print data from the beginning. This causes a problem in the printer that is the target, in that some of the print data will be sent twice, resulting in erroneous printing such as duplicate printing.
With a scanner, once the head has moved out, it is not possible to return the head to its original position to obtain the same data again. This raises a problem in that it is not possible to continue the data transfer after the occurrence of a bus reset, even if the initiator restarts the data transfer from the beginning.
Note that various techniques have been proposed in the art to resolve the inconveniences caused by the occurrence of bus resets, such as that disclosed in Japanese Patent Application Laid-Open No. 11-194902, by way of example. With this prior-art technique, when a bus reset occurs, data processing is held then restarted after the network configuration has been rebuilt.
However, transfer data is simply resent after a bus reset with this prior-art technique, and it is not possible to determine whether the resent transfer data is a resumption of transfer data that was sent before the bus reset occurred. The problem of duplicate printing can therefore not be solved by this prior-art technique.